text控件显示数字的问题！

Private Sub Command1_Click()
Dim a As Double
Dim b As Double
Dim c As Double
Dim a1 As Double
Dim b1 As Double
Dim c1 As Double
a = Val(Text1.Text)
b = Val(Text2.Text)
c = a - b

a1 = Val(Text4.Text)
b1 = Val(Text5.Text)
c1 = a1 - b1

x = (c + c1) / 2

Text7.Text = Str(Round(x, 4))
End Sub

例如：
a=69.2875 b=69.2782
a1=69.2875 b1=69.2777
显出的是0.0095 四舍六入应该是0.0096
请问高手怎么处理？？